Die-cast copper rotors as strategy for improving induction motor efficiency

This paper reviews the advantages of substituting copper for aluminum in the rotor squirrel cage as a central strategy toward reaching substantially higher efficiency. Short die life has discouraged production of copper rotors, but recent development of a heated nickel-base alloy die technology has solved the manufacturing problem; this is briefly reviewed. Copper rotor high efficiency motors are now commercially available. Performance characteristics of example motors are presented and design modifications employed to optimally utilize the high conductivity copper are outlined. Weight and cost savings realized by European manufacturers with high efficiency copper rotor motors compared to aluminum rotor designs with the same efficiency and performance characteristics are discussed. Applications for these motors in defense systems are now being examined for both 60 and 400 Hz equipment. Induction motors with copper rotors for traction also appear to have real advantages. Use of this motor type in the series hybrid drive system of a heavy duty Marine Corp truck is reviewed.